1. Field of the Invention
This invention relates generally to superconducting dynamoelectric machines, and more specifically, this invention relates to a superconducting dynamoelectric machine having an improved arrangement for supporting a cryogenic temperature portion of the rotor on an ambient temperature portion of the rotor.
2. Description of the Prior Art
Superconducting dynamoelectric machinery having a rotating superconductive field winding requires a stable support for the cryogenic portion of the rotor, while still limiting heat conduction from the ambient temperature portion of the rotor to the greatest extent possible. In prior art cryogenic structures (Dewar vessels), an outer ambient temperature structure has a fill tube passing through it to convey the cryogenic material to an inner cryogenic temperature portion. The fill tube is affixed to the ambient temperature structure to provide support for the cryogenic temperature portion. In addition, thin wires or spokes are utilized to help support the cryogenic temperature portion. The cryogenic temperature portion is surrounded by a vacuum to eliminate convection losses and the surfaces of the inner and outer walls are highly polished to lower radiation losses. Heat conduction to the cryogenic temperature portion is directly proportional to the cross-sectional area divided by the length of the supports linking the ambient temperature and cryogenic temperature portions. Long thin supports are therefore used to reduce conduction losses, which would otherwise result in excessive "boiloff" of the cryogenic material.
However, in a stationary Dewar vessel the support is only required to support the weight of the assembly and is not required to provide precision placement of the cryogenic temperature portion with respect to the ambient temperature portion. On the other hand in a rotating Dewar assembly, such as a cryogenic portion of the superconducting machine rotor, the cryogenic temperature portion must be supported for static and dynamic loads. The superconducting field winding located in the cryogenic temperature portion may have a significant mass. Thus, the supporting arrangement for the cryogenic temperature portion must: transmit machine torque from the field winding to the prime mover; maintain the concentricity of the ambient temperature and cryogenic temperature portions; absorb axial thermal distortion; and limit heat losses to the cryogenic temperature portion. One way to accomplish this is to use a tubular support for one end of the cryogenic temperature portion to provide the torque transmittal capability, while the other end is supported by spokes to absorb axial thermal distortion and limit heat losses. The use of such spokes is illustrated, for example, in U.S. Pat. No. 3,368,087 -- Madsen. However, high stresses would be developed in the spokes because of their thermal contraction when the cryogenic temperature portion is cooled to cryogenic temperature from ambient temperature. These high stresses raise the possibility of spoke breakage under dynamic loading conditions. Further, these stresses could lead to undesired repositioning of the cryogenic temperature portion with respect to the ambient temperature portion, thus raising the possibility of high unbalance forces during operation.